Topic: 69 FMX Crossmember DS/PS?

[Buiaka]

Hi all,

which side on the crossmember is the driver side? I think you can install it both directions, but the transmission is then not centered the right way.

Thank you

greets

Christopher

[specialed]

Isnt there an R stamped on right side as there is big R stamped on the C6 auto brace. 

[Buiaka]

"R" means then Passenger side?

[67gtasanjose]

"R" means then Passenger side?

"R" means RIGHT side and on L-Drive vehicles it is Passengers side.
Think about it this way...Which side is the auto trans vacuum modulator on? The crossmember is configured to clear that modulator on FMX and C-6 Mustangs/Cougars

[Buiaka]

Thank you,

just wanted to be sure.

greets

Christopher

[Buiaka]

To bring this up again. I know now the orientation of the fmx crossmember, but on the driversside i have two holes for the bolt to go in.
Do i have to install it to the lower or upper hole? I read something it should be the upper hole, correct?

Thank you

greets

Christopher

[J_Speegle]

To bring this up again. I know now the orientation of the fmx crossmember, but on the driversside i have two holes for the bolt to go in.
Do i have to install it to the lower or upper hole? I read something it should be the upper hole, correct?

Think it only will fit one way but it looks like I used the top one last time I did it.

Please ignore the mount bolts and washers. They were holing things in place for the moment

[Buiaka]

Thank you for the pictures. It seems that everything is correct on my car. I got the right crossmember (351 on underside and the R on the passenger side) and its installed the right way.
The silentblock is new. So thats not the reason for my vibrations on highway speed. The search goes on
Next will be the installation of a rebuilt third member and new axles with bearings.

Thank you

greets

Christopher

[WT8095]

So thats not the reason for my vibrations on highway speed. The search goes on

Did you check out the u-joints?

[Buiaka]

U-joints are new and the original driveshaft was checked, but no balance issues.
I tried an aluminium shaft with no difference. Engine was rebuilt to oem specs.
I had this vibrations before the rebuilt. Tranny and rear end is original to the car.
Had the tires balanced, tried different shops, no difference. Changed the tires from front to rear, no difference.
The vibes occur only at 70+ and get stronger the faster i go. When in neutral the vibes "fade" away fast. Not immediately, but go away.
Had some sloppy yoke in the tranny extension housing, so i changed the bushing and seal. No change ;(
Ill try a rebuilt third member and see if vibes are gone.

Greets

[WT8095]

You mentioned the yoke was sloppy. How much play is there in the splines? Could be torsional vibration if the splines are worn. Also, are the driveline angles OK? (less than 3 degrees)

[67gtasanjose]

...Ill try a rebuilt third member and see if vibes are gone.

You may be on the right track here...But I would want a "smoking gun" before just buying more exchange parts.

It is very difficult without special tools to locate a 3rd member or "pumpkin" noise if it is somewhat subtle. One special tool comes to mind that is called "Chassis Ears" and here is a video that shows some of it's uses. They can be RENTED.



or a quicker video...



My thoughts (as a professional mechanic) FIRST find and confirm the "noises" inside the differential or rear wheel bearings... with this tool you could save tons of money and time before you actually then have a tear-down inspection of the original (maybe by a qualified rebuilder). More often than not, a set of NEW BEARINGS in the 3rd or a single wheel bearing is all you need. (maybe a set of clutch plates if diff is a Limited Slip)

Worth looking into before pulling the trigger on the 3rd member.

Richard

[Buiaka]

Hi,

thank you all for the replies. When i bought the car it had hi-jackers and 2" lowering blocks installed on the rear.
So i thought that this could be the reason for the vibes, because the driveline angle was not correct.
I removed the lowering blocks and installed new shocks, again no difference at all.
Now everything on the car is correct how it was delivered 45 1/2 years ago. Original engine, FMX trans, 3.00 open third member.
With the engine rebuild we changed the motor mounts also.
The Motor sits in the correct height compared to my friends 1969 351W Mach1.
Why should the driveline angle not be correct? The removal of the 2" lowering blocks should have made a difference in noise and feeling.

greets

Christopher

[drummingrocks]

I'll second what 67gtasanjose said.  I'd want to find a definite problem before I started swapping parts, especially as expensive as another rear end will be.  And those Chassis Ear machines are great.  We use them all the time at our shop.  They really do work well, especially when you've exhausted all other means of finding a problem.

[WT8095]

Why should the driveline angle not be correct?

They should be correct, now. The lowering blocks, etc. was the type of thing I was getting at. Since you've put everything back to original, the angles should be good.

Based on your description of the problem and what you've tried, the splines on the yoke & output shaft would be on the top of my suspect list. But as others have pointed out, a thorough diagnosis will be less costly in the long run as opposed to swapping parts until the problem goes away.

This website has some good explanations of vibration issues:

http://www.machineservice.com/technical-101/vibrational-issues/